Uninterruptible power supply (UPS) systems are useful for protecting devices against power loss. UPSs typically have an input for an AC line source, rectification and boost circuitry, an inverter, and a battery. The UPSs can selectively supply power from either the AC line source to the load or from the battery to the load. When the battery is not being used to supply the load, it may be charged by power from the AC line source. The AC line source may be single phase or three phase, and UPSs exist that are configured to handle one or the other type of AC power. UPSs are typically configured to switch to battery if the input line voltage is beyond an allowable voltage range.
Various battery configurations may be used in UPSs, and battery charger failure may be detected so that failing UPSs can be repaired. UPSs may use single string or multi-string battery configurations. Single-string configurations typically provide a positive battery voltage and multi-string configurations typically provide positive and negative battery voltages. Which configuration a particular UPS has can be programmed into the UPS to help ensure proper operation of the UPS. The batteries can be monitored to detect failures and this is typically done by monitoring battery voltage and other parameters such as current flowing into or out of the battery, e.g., to determine if the battery has been exhausted. Batteries may drain, e.g., during storage due to leakage into battery bus capacitors and other components that are electrically connected to the batteries. Different UPSs, with different nominal battery bus voltages and/or different battery configurations typically have different battery packs. Further, replacing batteries or battery packs, at least for a mid-range capacity UPS (e.g., between about 3 KVA and about 10 KVA) typically involves disconnecting the UPS from the line source power and disassembling the UPS significantly to access the batteries/battery pack(s).
Various fault conditions may be detected and responsive actions taken. For example, inverter voltage may be monitored to detect load short circuits. If a short circuit is detected, the UPS may switch to bypass mode to connect the line source directly to the load. A UPS may also start in bypass mode so that an output short circuit is connected to the line source during startup, before the UPS has a chance to detect the short circuit.
Further, various components of UPSs can be replaced as they fail and/or as upgrades become available. For example, fans used to cool UPSs and/or microcontrollers used to control UPSs can be replaced by disassembling the UPSs.
Several factors influence aspects of UPS design, including growing demands for stable, reliable and continuous supply of electricity to sensitive electronic equipment and for increasingly compact devices to provide this power. There is a demand for power backup units to occupy a small amount of space and to provide significant amounts of stable power, e.g., to computers, servers, and other devices. UPSs provide backup power, but typically produce significant amounts of heat in doing so. To cool UPS components, one or more fans are often used to flow air through the UPS. Competing interests are that the cooling effect of the fans, as well as the noise and cost of the fans, is proportional to their size and number. The fans are typically inside a housing of the UPS and can be replaced by removing the UPS from its rack (if rack-mounted) and/or disassembling the UPS to access the fan.
As UPSs are used to provide continuous power to sensitive electronic devices, it is desirable that a UPS can be serviced/repaired without interrupting the power supplied to the electronic devices and without disturbing the physical location of the UPS. For example, it is desirable to replace a fan of a rack-mounted UPS without removing the UPS from the rack. Further, mid-range tower (stand-alone) or rack-mounted UPSs typically have large batteries/battery packs that require two or more people and/or lifting equipment to handle.